Voltage flip turns magnetism on, off
Peter Weiss
Ordinarily, a material that is magnetic stays that way. Only heat or stronger magnets can erase its magnetism. Now, however, researchers in Japan have made a material whose inherent magnetism can be turned off and on electrically. It takes just a flip of a switch, as long as the material stays ultracold.
The novel compound, a semiconductor, combines its extraordinary magnetic behavior with electronic properties well-suited for making microcircuits. That combination may lead to faster, lower-power devices for reading and writing magnetic data than those used today, scientists say. It might also help usher in microcircuits that exploit electrons' electric charges and also spin, a magnetic property of electrons (SN: 3/4/00, p. 155).
Hideo Ohno of Tohoku University in Sendai and his colleagues created a nonmagnetic compound of indium and arsenic. By adding manganese atoms to the mix, the researchers created mobile positive charges, called holes. These caused the manganese atoms, which act like tiny bar magnets, to collectively produce a magnetic field throughout the material.
To test electrical control of the material's magnetism, the scientists built a tiny transistor using several thin layers of materials, including the novel semiconductor. This layer lost its magnetism the instant the researchers applied a positive voltage to the device. The voltage drove the holes out of the layer, destroying the magnetic alignment of the manganese atoms, Ohno explains. A negative voltage makes the material magnetic again. They report their results in the Dec. 21/28, 2000 Nature.
A drawback of the new material is that it must be at a temperature of less than 30 kelvins to produce a magnetic field. However, scientists have begun formulating semiconductors with room-temperature magnetism. "This is very encouraging," Ohno says, although no one has yet demonstrated electrical control in those materials.
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References:
Awschalom, D.D., and R.K. Kawakami. 2000. Teaching magnets new tricks. Nature 408(Dec. 21/28):923.
Ohno, H., et al. 2000. Electric-field control of ferromagnetism. Nature 408(Dec. 21/28):944.
Further Readings:
Weiss, P. 2000. Electron spins pass imposing frontier. Science News 157(March 4):155.
______. 1999. New memories tap spin, gird for battle. Science News 155(April 3):223.
______. 1999. Puddle that spins together stays together. Science News 155(Jan. 16):39.
Sources:
Hideo Ohno
Laboratory for Electronic Intelligent Systems
Research Institute of Electrical Communication
Tohoku University
Katahira 2-1-1
Aoba-ku
Sendai 980-8577
Japan
From Science News, Volume 159, No. 4, January 27, 2001, p. 63.
